The olfactory system has several characteristics that make it favorable to study nerve cell development and replacement in the mammalian central nervous system. Olfactory neuroepithelium has the remarkable capacity to reconstitute olfactory receptor neurons. This is possible due to a persistent population of stem cells (neuroblast) that have the capacity to produce new neurons (neurogenesis) for the life of the individual. Thus, olfactory neurons are the exception to neuron dogma, and neuron replacement is possible, even in the adult. The factors that control neural regeneration of the olfactory system are not fully understood. The remarkable capacity of producing new neurons is of wide interest not only with respect for chemosensory function but also their use as a model system for the study of neuron replacement. There is still much to be learned about olfactory system regeneration and, transplantation techniques can provide a valuable approach to studying structure and function. Experiments are planned to remove olfactory receptor neurons from the nasal cavity and place them in different brain regions of neonatal and old age host animals. Anatomical, autoradiographic and immunocytochemical techniques will provide a comprehensive assessment of the capacity and limits of neurogenesis, nerve cell development, axon growth and plasticity of transplanted olfactory neurons. If donor neurons develop and integrate with host neural tissue, then the possibility of forming new synaptic connections exists. These provide a source of new neurons for the brain, a most significant finding. This project will contribute new information that will lead to a better understanding of the olfactory system and could provide the foundation for new strategies for treating neuron loss due to aging (smell, taste, hearing), injury and disease, such as Alzheimer's.